1. Field of the Invention
The present invention relates to an apparatus for assembling a floor in which a floor of a vehicle such as a motor vehicle is assembled by combining a plurality of workpieces which are made up of a front component constituting an engine room, a front floor constituting a floor surface of a vehicle compartment, a rear floor constituting a floor surface of a trunk room, or the like.
2. Description of Related Art
As this kind of apparatus for assembling a floor of a vehicle, there has been known the following. Namely, the apparatus comprises: a floor assembly station; a setting jig which is disposed in the floor assembly station and which positions and supports a plurality of workpieces constituting the floor of the vehicle; and a plurality of welding robots disposed on each lateral side of the floor assembly station, each of the welding robots having a welding gun mounted on an operating end thereof such that a plurality of workpieces on the setting jig are combined by welding to form the floor (see Published Unexamined Japanese Patent Application No. 193433/1992).
In this apparatus, the floor assembled in the floor assembly station is transferred by a transfer apparatus such as a transfer bar, or the like, to a station which lies ahead to perform the next step of assembling. By providing the transfer apparatus as explained above, the equipment cost becomes high.
There is also known the following apparatus in Published Examined Japanese Patent Application No. 6072/1989. In this apparatus, a welding robot is provided with a joint portion to which a workpiece holding device can be coupled. After the welding of the workpiece has been finished, the workpiece holding device is coupled to the joint portion and the workpiece is held by a plurality of clamping members provided in the workpiece holding device. The workpiece is thus transferred to the next station by the welding robot.
It is considered to apply this kind of art to the apparatus for assembling a floor. Namely, among a plurality of welding robots which are disposed on both lateral sides of the floor assembly station, one welding robot is provided with a joint portion to which a holding device for the floor can be coupled. After the assembling of the floor has been finished, the holding device is coupled to the joint portion. The floor is then supported by the holding device for transportation from the floor assembly station to the next station by means of a single welding robot.
However, since the floor is large in size and weight, it is difficult to stably transport it with a single welding robot. In addition, after the floor has been assembled, the holding device must be coupled to the joint portion before the floor is transported. Therefore, the time required to couple the holding device becomes a loss in time, with the result that the cycle time becomes longer. Alternatively, if the holding device is kept coupled to the welding robot, the holding device interferes with the floor during the assembly work of the floor. Therefore, the holding device must be removed out of the welding robot during the assembly work.
In view of the above-described points, the present invention has an object of providing an apparatus for assembling a floor of a vehicle in which the floor can be transported with welding robots, whereby the equipment cost can be reduced by deleting the transporting apparatus.
In order to attain the above and other objects, the present invention is an apparatus for assembling a floor of a vehicle, comprising: a floor assembly station; a setting jig which is disposed in said floor assembly station and which positions and supports a plurality of workpieces constituting the floor of the vehicle; a plurality of welding robots disposed on each lateral side of the floor assembly station, each of the welding robots having a welding gun mounted on an operating end thereof such that a plurality of workpieces on the setting jig are combined by welding to form the floor; wherein at least two welding robots on each lateral side of the floor assembly station, i.e., a total of four welding robots, among the welding robots disposed in the floor assembly station, are provided on each operating end thereof with a workpiece receiving member in a certain positional relationship with the welding gun, whereby the four welding robots are constituted into dual-purpose welding robots for both welding and transporting; and wherein the floor is transported by cooperation of the dual-purpose welding robots from the floor assembly station to a subsequent station in which a subsequent assembling step is performed, the floor being transported in a state of being supported through the workpiece receiving members at least at four longitudinal and lateral positions of the floor.
According to the present invention, at least two welding robots on each lateral side of the floor assembly station, i.e., a total of four welding robots, are constituted into dual-purpose welding robots for performing both welding work and transporting work, and the floor is supported through the workpiece receiving member at least at four longitudinal and lateral positions. Therefore, even if the floor is large in size and weight, it can be transported in a stable manner. In addition, since the workpiece receiving members may support only part of the floor, they can be formed small in size. Therefore, even in a state in which the workpiece receiving member remains mounted on the operating end of the robot, the assembly work of the floor can be performed without interference of the workpiece receiving member with the floor. Right after the floor has been assembled, the floor can be supported by the workpiece receiving members and can therefore be quickly transported.
The floor is provided with a jack-up point at each of four longitudinal and lateral positions, the jack-up point being for applying a jack at the time of jacking up the vehicle. Since the jack-up point is high in rigidity, the stability in supporting the floor improves if each of the workpiece receiving members of the dual-purpose welding robots supports each of the jack-up points of the floor. In this case, it is preferable to arrange the workpiece receiving member of at least one of the dual-purpose welding robots to support a corresponding jack-up point by aligning the corresponding jack-up point in both longitudinal and lateral directions, to thereby prevent the floor from deviating in position during transportation.
Preferably, the welding gun is mounted, through a supporting frame, on a wrist of three-axis construction provided at a front end of a robot arm of each of the dual-purpose welding robots, wherein the supporting frame is made up of: that first side frame on one side which extends in a longitudinal direction at a right angle to an axis of rotation of a wrist member provided at a front end of the wrist and which is coupled to the wrist member; a second side frame on a side opposite to, and parallel with, the first side frame; and cross members which combine both the first and second side frames, wherein the welding gun is mounted between the first and second side frames such that a gun arm projects in one longitudinal direction of the first and second side frames, and wherein the workpiece receiving member is fixed to an outer side surface of the second side frame. According to this arrangement, when the floor is supported, the load which operates on the workpiece receiving member is received by the supporting frame. Therefore, the load from the workpiece receiving member does not operate on the welding gun, thereby preventing the welding gun from being adversely affected. In addition, the workpiece receiving member is fixed to that surface of the supporting frame which faces the direction different from the direction in which the gun arm projects. Therefore, the welding work of the workpiece can be performed without interference of the workpiece receiving member with the workpiece. Also, the workpiece can be supported through the workpiece receiving member without interference of the gun arm with the workpiece.
Further, preferably, a position of fixing the workpiece receiving member is set such that, when the floor is supported by the workpiece receiving member, an operation line of a load to operate on the workpiece receiving member coincides with a vertical plane which includes the axis of rotation of the wrist member. The wrist member can thus be prevented from being subject to a moment of rotation when the workpiece is supported. The stability in supporting the workpiece can advantageously be improved.
When the welding work has been repeated, the electrode tip (i.e., the front end of the electrode) of the welding gun will get out of shape. Therefore, it becomes necessary dress (or reform) the electrode tip from time to time. As a conventional method of dressing the electrode tip of a welding robot which performs only the welding work of a workpiece, there is disclosed the following art in Japanese Published Unexamined Patent Application No. 228678/1989. Namely, an electrode tip dressing device is disposed close to a position in which a welding robot is disposed. While the workpiece is being transported after the welding work of the workpiece has been finished, the welding robot is operated such that the electrode tip of the welding gun comes into contact with the electrode tip dressing device, whereby the electrode tip is dressed. However, in that dual-purpose welding robot of the present invention which performs the welding work and the transporting work, the dressing of the electrode tip cannot be performed while the workpiece is being transported. Therefore, a time for electrode tip dressing must be separately reserved, resulting in a hindrance to an attempt to improve the workability. In this case, preferably, the apparatus further comprises travel bases which are provided so as to be reciprocated between the floor assembly station and the subsequent station, each of the dual-purpose welding robots being mounted on each of the travel bases; an electrode tip dressing device which is movable together with each of the travel bases, wherein, when each of the travel bases is moved from the subsequent station back to the floor assembly station, each of the dual-purpose welding robots is operated such that a welding electrode of each of the welding guns contacts each of the electrode tip dressing devices to thereby dress each of the electrode tips. It is thus not necessary to separately reserving a time for electrode tip dressing. The productivity can thus be improved.
Conventionally, there is known the following prior art in Japanese Published Unexamined Patent Application No. 193433/1992. Namely, each workpiece which is made up of a front component, a front floor, and a rear floor is transported by a transporting means into a workpiece feeding section which is located above one lateral side of a floor assembly station. They are then transferred by each of transfer means onto a setting jig in a predetermined positional relationship with one another.
In this prior art, each of the transfer means is made up of: a lifting frame which is moved up and down along supporting columns which are vertically provided on the other lateral side of the floor assembly station; a movable frame which can be shifted between a position right above the floor assembly station and said one lateral side of the floor assembly station and which is supported by the lifting frame; and a holding device which is suspended from the movable frame so as to be movable back and forth. Each of the workpieces transported into the workpiece feeding section is picked up from the transporting means by holding it with the holding device. Thereafter, by the movement of each of the movable frames, each of the workpieces is shifted to a position right above the floor assembly station, and is then lowered by the movement of the lifting frame. Then, by the back and forth movement of the holding device, each of the workpieces is aligned so as to be in a predetermined positional relationship with one another, thereby setting each of the workpieces onto the setting jig. In this prior art, however, each of the transfer means must be constituted as an exclusive equipment (i.e., equipment which is used only for a specific workpiece). This results in a higher equipment cost. In addition, on both lateral sides of the floor assembly station, there are disposed welding robots for combining by welding the workpieces on the setting jig. In this prior art, there are vertically disposed, on the other side of the floor assembly station, supporting columns for the transfer means. Therefore, there is a disadvantage in that the movable range of the welding robots to be disposed on the other side is restricted.
In such a case, preferably, the apparatus further comprises: transporting means for transporting three workpieces of a front component, a front floor, and a rear floor which constitute the floor of the vehicle into a workpiece feeding section which is located above one lateral side of the floor assembly station; an overhead frame which is provided above the other lateral side of the floor assembly station; three transfer robots for three workpieces of the front component, the front floor, and the rear floor, disposed on the overhead frame in a longitudinally spaced relationship from one another, each of the transfer robots comprising: a rotary base rotatable about a vertical axial line; a first arm coupled to the rotary base through a first joint; a second arm swingably coupled to a front end of the first arm through a second joint; a wrist of three-axis construction at a front end of the second arm; and a workpiece holding device for holding each of the workpieces attached to the wrist, wherein each of the workpieces transported into the workpiece feeding section: is picked up by each of the transfer robots; is rotated by the movement of the rotary base of each of the transfer robots into a position which lies above a free space between the workpiece feeding section and the overhead frame; is lowered through the free space for alignment into a predetermined positional relationship with one another in a position right above the setting jig; and is put in position onto the setting jig. According to this arrangement, a six-axis general-purpose robot can be used as the transfer robot. Therefore, there is no need of constituting the transfer means as an exclusive equipment, resulting in a lower equipment cost. Further, since the transfer robot is disposed on the overhead frame, the movable range of the welding robot to be disposed on the side portion of the floor assembly station can be secured wide enough in the free space below the overhead frame.
As an alternative arrangement, the following may also be considered. Namely, after each of the workpieces which are transported into the workpiece feeding section is picked up by each of the transfer robots, each of the workpieces is laterally moved by the movements of the first and second arms of each of the transfer robots into a position which lies above the free space between the workpiece feeding section and the overhead frame, and is then lowered through this free space. However, if a general-purpose small robot with a short arm length is used to reduce the weight and cost of the transfer robot, the workpiece holding device and the workpiece will interfere with the first joint of the transfer robot when the workpiece is moved laterally. As a result, the workpiece cannot be set in position onto the setting jig.
On the other hand, if the workpiece is moved by rotation of the rotary base into the position above and facing the free space as described above, even if a small general-purpose robot is used as the transfer robot, the workpiece and the workpiece holding device can be moved to the free space, while keeping them away from the first joint, by extending the first arm and the second arm. In this manner, the workpiece can be transferred to the setting jig through the free space without interference with the first joint.